Abstract

Self-phase modulation (SPM) in a Kerr medium has been widely used to spectrally chirp and broaden an optical pulse for pulse compression.¹ To compress a high-energy pulse directly, spectrally broadening and chirping the pulse by SPM in a bulk material is necessary. However, the nonuniform beam's spatial profile results in the spatial chirping effect. A stable optical resonator can be used as a large-scale, periodic waveguide for multipass SPM in a bulk medium. We show that a resonator can tolerate a round-trip B integral (maximum on axial, nonlinear phase shift) of 3.6 and still be stable. The calculated results show that the temporal SPM is able to accumulate through multiple passes while the growth of the spatial chirping is restrained. In 10 round trips, the total B integral that is useful for SPM can be as high as ~36, but the effective B integral associated with spatial chirping remains at 1.13. Experimental results of multipass SPM in a Nd-glass regenerative amplifier² confirm the calculations. The total B integral useful for SPM is found to be ~30. We have studied the switched-outbeam sizes of amplified pulses of short and long durations, which correspond to the cases with and without the self-focusing effect, respectively. We have deduced the effective B integral associated with spatial chirping tobe <1. Such multipass self-phase modulation in an intracavity bulk medium combines the advantages of the confinement characteristics of waveguides and the high power-handling capabilities of bulk media.

© 1990 Optical Society of America